A friend and I both demo'd stompers. I'm 190 5'9" and was in the 90, he's 165 6'2" and was in the 80. I put a jackson seat pad in before even hitting the water, I had found that necessary in my Jefe Grande. I agree with you that the Stomper on the showroom floor feels too big and tall. However, long story short, we both are going with the 90.
After getting on the water I didn't feel the 90 was too big at all and in fact boated shorter, easier and more responsive than the Grande. I slinked into some holes nice and slow and sideways, and that sold me on having the extra volume. The stern grabbed in and shot out. At 165, he was right on the lines of the 80. Any more weight and it would have looked over laden. He agreed it felt low and sunken. He's coming from a Nomad 8.5, so the gallons should be the same.
If you get a chance to demo, or even if not, go for the big one if you are over 165lbs and boost the seat if it feels too low or too big. BTW, this made a huge difference for me in my Jefe as well. Before boosting my Jefe seat I hated it.